Presently various fluids are used for heat transfer. The suitability of the heat-transfer fluid depends upon the application process. For example, some electronic applications require a heat-transfer fluid which is inert, has a high dielectric strength, has low toxicity, good environmental properties, and good heat transfer properties over a wide temperature range. Other applications require precise temperature control and thus the heat-transfer fluid is required to be a single phase over the entire process temperature range and the heat-transfer fluid properties are required to be predictable, i.e., the composition remains relatively constant so that the viscosity, boiling point, etc. can be predicted so that a precise temperature can be maintained and so that the equipment can be appropriately designed.
Perfluorocarbons, perfluoropolyethers, and some hydrofluoroethers have been used for heat-transfer. Perfluorocarbons (PFCs) can have high dielectric strength and high resistivity. PFCs can be non-flammable and are generally mechanically compatible with materials of construction, exhibiting limited solvency. Additionally, PFCs generally exhibit low toxicity and good operator friendliness. PFCs can be manufactured in such a way as to yield a product that has a narrow molecular weight distribution. They can exhibit one important disadvantage, however, and that is long environmental persistence.
Perfluoropolyethers (PFPEs) exhibit many of the same advantageous attributes described for PFCs. They also have the same major disadvantage, i.e., long environmental persistence. In addition, the methods developed for manufacturing these materials can yield products that are not of consistent molecular weight and thus can be subject to performance variability.
Hydrofluoropolyethers (HFPEs), a class of hydrofluoroethers (HFEs), can exhibit some of the same advantageous attributes of PFCs, but differ greatly in two areas. To their credit, they can exhibit markedly lower environmental persistence, yielding atmospheric lifetimes on the order of decades rather than millennia. However, some of the HFPEs taught as heat-transfer fluids can be a mixture of components of widely disparate molecular weight. Thus, their physical properties may change over time which makes it difficult to predict performance.